The present invention relates to a structural assembly that transmits and measures linear forces along and moments about three orthogonal axes. More particularly, a structural assembly is disclosed having structural elements connected with elliptical fillets to minimize stress concentration and interchangeable sensing elements with very low cross talk or the likelihood of affecting the reading in one axis from loads in another axis.
Transducers or load cells for determining rotational loads and axial loads about and along three orthogonal axes have been known. Two such load cells are disclosed in U.S. Pat. Nos. 4,640,138 and 4,821,582. U.S. Pat. No. 4,640,138 illustrates a multiple axis load-sensitive transducer having inner and outer members that are joined by a pair of axially spaced spiders. The spiders comprise arms that are integral with the inner member and are connected to the outer member by flexible straps that have longitudinal lengths with the ends of the straps fixed to the outer member. The arms of the spiders are fixed to the center of the associated strap. Loads are sensed as a function of bending on the spider arms.
U.S. Pat. No. 4,821,582 illustrates a load transducer that measures linear forces in three axes and moments about two of the axes. The transducer has inner and outer structures connected by load-sensitive spider arms or shear beams. The outer ends of the spider are connected to outer lengths which are stiff when the inner structure is loaded in a direction along an axis perpendicular to the plane of the spider.